In known manner, such a drive device comprises a transmission gearbox with a reduction ratio associated with a plate for fixing to the moving machine tool element, the inlet to the gearbox being coupled to a motor and its outlet being formed by two gearwheels or pinions turning synchronously and meshing with a rack secured to the structure of the machine tool and extending parallel to the direction of rectilinear movement.
This outlet via two gearwheels makes it possible to take up slack continuously by introducing into the transmission system connected to the two gearwheels a torque that tends to turn them in opposite directions, thereby guaranteeing a degree of precision in the amplitude of the rectilinear movement performed and in the positions of its tool attachment points.
In a known device of that type, the drive system comprises an inlet shaft acting via two angle takeoffs in series on said shaft to drive each of the inlet shafts of respective reducing sleeves whose outlets carry the above-mentioned gearwheels or pinions. The preloading is obtained by a torsion bar which forms a part of the inlet shaft between the angle takeoffs. The magnitude of the preloading is fixed when the device is installed on the machine tool with the pinions being engaged with the rack, by applying torsion to the bar which is accessible from an end of the device opposite from the drive moor, and by constraining one and/or both angle takeoffs in rotation on said prestressed bar.
The architecture of that device leads to a certain number of drawbacks in the sense that it constitutes a limit on standardizing manufacture of its components and it limits the stiffness of the transmission which needs to be as high as possible for controlling movement with precision.